lkml.org 
[lkml]   [2011]   [Nov]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 8/9] readahead: basic support for backwards prefetching
On Wed 30-11-11 08:37:16, Wu Fengguang wrote:
> (snip)
> > > @@ -676,6 +677,20 @@ ondemand_readahead(struct address_space
> > > }
> > >
> > > /*
> > > + * backwards reading
> > > + */
> > > + if (offset < ra->start && offset + req_size >= ra->start) {
> > > + ra->pattern = RA_PATTERN_BACKWARDS;
> > > + ra->size = get_next_ra_size(ra, max);
> > > + max = ra->start;
> > > + if (ra->size > max)
> > > + ra->size = max;
> > > + ra->async_size = 0;
> > > + ra->start -= ra->size;
> > IMHO much more obvious way to write this is:
> > ra->size = get_next_ra_size(ra, max);
> > if (ra->size > ra->start) {
> > ra->size = ra->start;
> > ra->start = 0;
> > } else
> > ra->start -= ra->size;
>
> Good idea! Here is the updated code:
>
> /*
> * backwards reading
> */
> if (offset < ra->start && offset + req_size >= ra->start) {
> ra->pattern = RA_PATTERN_BACKWARDS;
> ra->size = get_next_ra_size(ra, max);
> if (ra->size > ra->start) {
> /*
> * ra->start may be concurrently set to some huge
> * value, the min() at least avoids submitting huge IO
> * in this race condition
> */
> ra->size = min(ra->start, max);
> ra->start = 0;
> } else
> ra->start -= ra->size;
> ra->async_size = 0;
> goto readit;
> }
Looks good. You can add:
Acked-by: Jan Kara <jack@suse.cz>
to the patch.

Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR


\
 
 \ /
  Last update: 2011-11-30 12:25    [W:0.185 / U:0.444 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site